For over 100 years asphalt was laboriously mined in the underground asphalt mines of La Presta and exported all over the world for road construction. Today the mines are no longer in operation and are partially open to the public as a museum.
If brooks and rivers run only sluggishly above ground, hydropower is nearly impossible to harness. That is why the inhabitants of the valley of Le Locle began to use subterranean streams. This is how the cave mills of "Col-des-Roches" arose.